*{
    margin: 0;
    padding: 0;
}
body{
    background: azure;
}

/* 小广告 */
.ad{
    display: none;
    position: fixed;
    bottom: 20px;
    right: 20px;
    z-index: 100;
    width: 200px;
    height: 200px;
    background-image: url(images/ad.png);
    background-size: cover;
    border-radius: 10px;
    transition:.3s;
}
.ad a{
    position: absolute;
    left: 45px;
    bottom: 17px;

    width: 110px;
    height: 40px;
    color: #000;
    text-align: center;
    text-decoration: none;
    line-height: 40px;
    background: #fff;
    border-radius: 10px;
}
.ad img{
    position: absolute;
    left: 163px;
    bottom: 162px;
}